What is Laryngeal Hemiplegia?
Laryngeal hemiplegia is a common respiratory disorder that is most frequently seen in tall, male horses in athletic occupations. In this disorder, damage or disintegration occurs to one or both of the recurrent laryngeal nerves, the nerves responsible for the movement of the arytenoid cartilages. In most cases, it is just the left nerve, and therefore the left arytenoid cartilage, that is affected. When the arytenoid cartilage becomes paralyzed, it can no longer move out of the way of the trachea and becomes an obstruction to air flow. This leads to poor performance in the horse as well as the characteristic whistling or roaring, particularly after strenuous exercise.
Laryngeal hemiplegia is a common respiratory disorder in equines in which the arytenoid cartilage in the larynx becomes paralyzed and interferes with the flow of air from the trachea.
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Symptoms of Laryngeal Hemiplegia in Horses
The symptoms of laryngeal hemiplegia are often very subtle until the horse begins to exert itself. A growing intolerance of regular exercise, a slight shrinking of the throat latch, and an alteration in the whinny may be the only clues until the horse starts to exercise. Once the animal begins exerting itself, the condition becomes more noticeable as the characteristic whistling or roaring sound is created by airflow over the paralyzed cartilage that is obstructing the larynx.
- Whistling sound upon exertion
- Poor performance in the horse during exercise
Several components of the horse's body are involved in this disorder. They include:
- Arytenoid cartilage - This pair of pyramid-shaped forms are located within the larynx itself and are responsible for vocal sound; they are each controlled by a recurrent laryngeal nerve
- Larynx - This structure, which divides the trachea and the esophagus, is the located in the back of the throat and it also connects the nasal passages to the windpipe
- Recurrent laryngeal nerve - This is the nerve that is responsible for controlling the arytenoid cartilage. Degeneration or damage to this nerve causes the paralysis in the arytenoid cartilage; the left recurrent laryngeal nerve is more prone to degeneration than the right nerve
Causes of Laryngeal Hemiplegia in Horses
The reasons that a horse may develop laryngeal hemiplegia are poorly understood, but genetic susceptibility is thought to play a role, and it most often attacks performance breeds such as Thoroughbreds, Standardbreds, the American Quarterhorse, and many draft horses. Other possible causes of laryngeal hemiplegia include trauma to the recurrent laryngeal nerve and lead poisoning. Equines between the ages of three and seven are the most likely to develop this order, and males over fifteen hands high are more susceptible to this disorder.
Diagnosis of Laryngeal Hemiplegia in Horses
This disorder is not usually particularly difficult to diagnose, at least when the animal is showing clinical signs. The whistling and roaring sounds are fairly distinctive, and a confirmation of the disorder can be shown utilizing a standing or a treadmill endoscopy. Laryngeal hemiplegia is further evaluated by grade to help determine the next step in the treatment of the disorder:
- Grade 1 - Movements on both sides of the larynx are synchronized
- Grade 2 - Major movements of the larynx are usually synchronized, but transient inconsistencies may occur
- Grade 3 - One side of the arytenoid cartilage, usually the left, has reduced functionality; the affected arytenoid can be pressed back into action by holding the nostrils closed, but it is only temporary
- Grade 4 - The paralyzation of the arytenoid cartilage that is affected is nearly complete and occasionally the cartilage from the other side of the larynx may sometimes cross the midline when compensating for the inaction of the paralyzed side
- Grade 5 - This is the complete paralyzation of the arytenoid cartilage
Treatment of Laryngeal Hemiplegia in Horses
There are several options available to treat severe cases of laryngeal hemiplegia for horses. Some of the better-known options include:
This surgery is utilized more frequently than any other as it is successful in 70-90% of horses. Also known as a tie-back surgery, the small incision is made in the throat latch and the paralyzed cartilage is tied back into an open position through the incision. A large percentage of horses with competitive or strenuous jobs are able to go back to their previous levels of work after this corrective surgery has been allowed to heal fully.
Also known as a cordectomy, this procedure removes both the vocal cord and ventricle on the side that is affected by paralysis in order to widen the airway and is often used in conjunction with a prosthetic laryngoplasty. The surgery is done using a laser that is passed through the nasal passages and is only 20-30% effective by itself. Unlike the other operations, ventriculectomy does not require any incision or anesthesia when employed by itself, so is less invasive.
This surgery is usually reserved for horses who have already had a failed prosthetic laryngoplasty, and it is the complete removal of the paralyzed arytenoid cartilage. Horses who have undergone this procedure are not as likely to return to their previous level of ability and have a higher risk of complications.
Recovery of Laryngeal Hemiplegia in Horses
The prognosis for this disorder is usually fairly good. Athletic performance almost always improves after successful surgery, although not always to the same level as before the disorder emerged. Even racehorses who develop this disorder are often able to successfully go back to work after an uncomplicated prosthetic laryngoplasty. After surgery, the patient will usually remain in the hospital for 24-48 hours for observation and to have the proper antibiotics and pain management medications administered. Patients are often confined to a stall with hand walking or other exercise restrictions during the healing period, generally around eight weeks. Possible complications that may occur postoperatively include infection, implant failure, chronic cough, or chronic aspiration of feed.
Laryngeal Hemiplegia Questions and Advice from Veterinary Professionals
I see that postop complications can include chronic cough and aspiration of feed. Our horse has just been diagnosed with left recurrent laryngeal nerve paralysis - there has been no whistling sound upon exertion nor poor performance when exercised ( although his exercise is only pleasure riding on the trails ) but he chokes and coughs often when eating and or drinking. Scoping detected some debris - I am sorry cannot remember exactly where ( trachea ) and a lung flush detected small airway disease ( mild and recent ). Has been on Prednisolone for 5 weeks.
He doesn't exactly fit the description of left recurrent laryngeal nerve paralysis. He is a 14 year old rocky mountain horse otherwise healthy. I am confused.
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